Offshore jackup rigs have been widely employed in offshore exploration for oil or gas. The jackup rigs usually comprise a jackup unit (JU) including a hull with a top platform for providing a working area and accommodating various working instruments. One common instrument employed on the top platform of a JU in an offshore jackup rig is cantilever.
In the current operation of a cantilever, only one stern pad and one hold-down claw are used for one beam of a cantilever. The hold-down claw used is a fixed type, meaning that the hold-down claws are welded to a fixed claw body being permanently installed onto the top platform of the hull of a jackup rig; thus, the hold-down claws can take the uplift load from the cantilever. Since the hold-down claws are permanently installed, it can only be removed by a destructive way such as cutting.
In the offshore exploration, jackup rigs have been employed for many purposes including drilling, accommodation, decommissioning, well intervention, and plug and abandonment (P&A). A rig capable of serving all the purposes with optimized cantilever outreach, load capacity and main deck space is always preferred. However, the optimized rig main deck arrangement and cantilever capacity are always different for different purposes. The characteristics of the fixed hold-down claws postulate a limit on the sizes and types of the cantilevers that can be installed. Furthermore, the fixed hold-down claws restrict the maximum extension of a given cantilever. There is no way to change a different type of cantilever or a cantilever with a different size without incurring major modifications of a rig.
Therefore, there is an imperative need to develop a JU that is so versatile that different types of cantilevers with different sizes can be flexibly chosen according to the different serving purposes. The installed cantilever maximum outreach for the serving purpose can be further improved when less load capacity is required; or the cantilever maximum load capacity can be further improved when less outreach is necessary.